Updated guidelines designed to prevent nosocomial transmission of diseases inject some new uncertainties in the efforts to protect health care workers.

For years, hospitals have relied on the "3-foot rule" — the concept that caregivers need to use droplet precautions if they are within 3 feet of a patient. That has given way to a 6-foot recommendation and an acknowledgement that little is known about the range of infectivity.

The Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings 2007, a set of influential recommendations issued by the Centers for Disease Control and Prevention, also recognizes that some "opportunistic" infectious agents that are not typically airborne may be transmitted via aerosolized particles.

But the passages that are causing concern for some health care worker advocates involve the use of masks and respirators for protection of health care workers. For example, one passage seems to imply that annual fit-testing may not be necessary: "The optimal frequency of fit-testing has not been determined; retesting may be indicated if there is a change in facial features of the wearer, onset of a medical condition that would affect respiratory function in the wearer, or a change in the model or size of the initially assigned respirator."

The guideline does not specify that the U.S. Occupational Safety and Health Administration requires annual fit-testing of filtering face-piece respirators, such as N95s. In fact, in July, Congress let the so-called Wicker Amendment expire. Proposed by Rep. Roger Wicker (D-MS), it prohibited OSHA from using federal funds to enforce the annual fit-testing rule for tuberculosis.

"It's an incredibly equivocal document," says Bill Borwegen, MPH, occupational safety and health director of the Service Employees International Union (SEIU). "It seems only natural that you should err on the side of caution and the precautionary principle and not err on the side of danger."

Yet Michael Bell, MD, associate director for infection control at CDC's Division of Healthcare Quality Promotion (DHQP), insists that the agency incorporated occupational health input and sought to bridge the difference of opinion between infection control professionals and industrial hygienists as it drafted the isolation guideline.

"We agree completely with the precautionary principle," which states that in the absence of scientific data, facilities should err on the side of protections for health care workers, says Bell. "The dichotomy is a little bit outdated. We're finding that industrial hygiene and infection control are overlapping increasingly these days."

Bell noted that DHQP has hired its first industrial hygienist, a prior employee of the National Institute of Occupational Safety and Health, to provide that in-house perspective.

"The isolation guideline agrees with NIOSH recommendations," says Bell. "It recommends that for respiratory protection, we require a fit-tested N95 respirator certified by NIOSH, a program for respiratory health training and instruction in self-fit-check."

NIOSH supports annual fit-test

When the isolation guidelines were released, the SEIU and the AFL-CIO sent a joint letter to NIOSH director John Howard, MD, MPH, JD, LLM, asking for NIOSH's position on the scientific evidence supporting annual fit-testing and the distinction, if any, between airborne infectious diseases and other airborne particles.

In an 11-page letter, Howard responded: "NIOSH supports the current legal requirement that follow-up respirator fit testing be performed annually for employers covered by OSHA's Respiratory Protection Standard and believes that OSHA has shown that the current best scientific, and practical, evidence supports an annualized periodicity for follow-up respirator fit-testing across all covered industries."

Howard noted that NIOSH is conducting research on the changes in fit over time that might have implications for fit-testing. That data collection will end in 2010.

NIOSH also is developing new criteria for respirators which will improve their overall fit characteristics. However, Howard noted that the fit criteria will not alter the need for individual fit-testing to ensure that the respirator fits the user.

As for the behavior of aerosolized infectious particles, Howard said, "NIOSH also believes that particles of the same size, regardless of whether the particle is infectious or not infectious, will exhibit the same aerodynamic behavior and should be treated in the same manner with regard to respiratory protection and fit testing."

In other words, the same rules that apply to industrial respiratory protection are pertinent for health care.

Bell insists that CDC has accepted basic aerodynamic principles, and that the isolation guideline reflects that. For example, in contrast to previous definitions of infectious droplets, the guideline states, "Observations of particle dynamics have demonstrated that a range of droplet sizes, including those with diameters of 30μm or greater, can remain suspended in the air."

Yet aerosolized particles do not necessarily remain infectious, and therein lies the difference between infectious agents and an industrial hazard, such as coal dust, says Bell. "There are many reasons why these particles change over time and lose their infectivity," he says.

DHQP is not in conflict with NIOSH, he says. "Our relationship with NIOSH has been very good for the last couple of years," Bell says. "The irony is that both groups have the same goal. They just use different words. Some of the philosophical issues might seem different. When you parse it down to actual intent and practices, they end up being very similar."

When there is a question about transmission patterns of a particular disease, such as SARS or pandemic influenza, the guideline recommends using an N95, he notes. It also recommends an N95 for aerosolizing procedures, such as intubation or bronchoscopy.

That guidance is not strong enough to reassure health care workers that they will be protected an emerging infectious disease, Borwegen charges. "The bottom line, at the end of the day, is that because of this kind of lack of protection, if we have a pandemic situation, workers are not going to go to work because they're going to be scared," he says. "I don't know what purpose this serves to not practice the precautionary principle and not to protect people from these particles."